Iterative data-aided carrier frequency offset estimation for code division multiple access systems

ABSTRACT

Iterative data-aided carrier CFO estimation for CDMA systems. Any communication receiver may be adapted to perform the iterative data-aided carrier CFO estimation. The iterative data-aided carrier CFO estimation is performed using a high accuracy method. The operation may be described as follows: a received signal is despread and buffered. Using the received preamble sequence, an initial estimate of the CFO is obtained. This estimate is used to correct the whole despread data. The corrected data using the initial CFO estimate is sliced. Each despread data symbol is divided by the corresponding sliced data decision. The obtained sequence is then averaged across different codes to obtain a less noisy sequence, which is then used to estimate the CFO again. The procedure can be repeated (iterated) to obtain a more accurate carrier frequency offset estimate; the number of times in which the procedure is repeated may be programmable or predetermined.

CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS ContinuationPriority Claim, 35 U.S.C. § 120

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. § 120, as a continuation, to the following U.S. Utility PatentApplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

1. U.S. Utility application Ser. No. 10/114,565, entitled “Iterativedata-aided carrier frequency offset estimation for code divisionmultiple access systems,” filed Apr. 2, 2002 now U.S. Pat. No.7,139,339.

Incorporation by Reference

The following U.S. Utility Patent Application is hereby incorporatedherein by reference in its entirety and is made part of the present U.S.Utility Patent Application for all purposes:

1. U.S. Utility patent application Ser. No. 10/114,800, entitled“Carrier frequency offset estimation from preamble symbols,” filed Apr.2, 2002, pending.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention relates generally to communication systems; and, moreparticularly, it relates to communication receivers employing CodeDivision Multiple Access (CDMA).

2. Description of Related Art

Data communication systems have been under continual development formany years. There is oftentimes difficulty in accommodating the offsetof operational frequencies between various devices within thecommunication system. Carrier frequency offsets (CFOs) are very commonin data communications systems. When there is a frequency offset betweena transmitter and a receiver within a communication system, there may besignificant degradation in performance. The undesirable degradation inperformance may result in an inability to demodulate and decode receiveddata.

In order to correct for CFOs, an accurate estimate of the CFO is needed.In packet systems, a known preamble sequence is transmitted with eachdata packet. The received sequence and the known preamble are usuallyused at the receiver to estimate the CFO. The prior art includes anumber of various methods and approaches that may be used to achieve aCFO. However, these prior art methods and approaches typically involve ahigh degree of computational complexity. In addition, these prior artmethods and approaches often fail to provide for a high degree ofaccuracy. As such, accurate CFOs may typically not be achieved in mostprior art communication systems. This results in a failure to achieveoptimal performance and accurate system operation.

One particular type of communication system, a cable modem (CM)communication system, has been under continual development for the lastseveral years. There has been development to try to provide forimprovements in the manner in which communications between the CM usersand a cable modem termination system (CMTS) is performed. Many of theseprior art approaches seek to perform and provide broadband networkaccess to a number of CM users.

CM communication systems are realized when a cable company offersnetwork access, typically Internet, access over the cable. This way, theInternet information can use the same cables because the CMcommunication system puts downstream data, sent from the Internet to anindividual computer having CM functionality, into a communicationchannel having a 6 MHz capacity. The reverse transmission is typicallyreferred to as upstream data, information sent from an individual backto the Internet, and this typically requires even less of the cable'sbandwidth. Some estimates say only 2 MHz are required for the upstreamdata transmission, since the assumption is that most people download farmore information than they upload.

Putting both upstream and downstream data on the cable television systemrequires two types of equipment: a cable modem on the customer end andthe CMTS at the cable provider's end. Between these two types ofequipment, all the computer networking, security and management ofInternet access over cable television is put into place. Thisintervening region may be referred to as a CM network segment, and avariety of problems can occur to signals sent across this CM networksegment.

One particular deficiency that may arise within the CM network segmentis the undesirable introduction of a CFO in the expected clock frequencysent from the CMs within the CM communication system to the CMTS. Theredo exist some approaches in the prior art to try to estimate this CFO,but these prior art approaches typically fail to provide an efficientsolution. As in the general prior art application of trying to performCFO estimation, these prior art methods and approaches typically involvea high degree of computational complexity. In addition, these prior artmethods and approaches often fail to provide for a high degree ofaccuracy. In order to correct for CFOs, an accurate estimate of the CFOis needed. In packet based communication systems, a known preamblesequence is transmitted with each data packet. The received sequence andthe known preamble are usually used at the receiver side to estimate thecarrier frequency offset. However, in many cases, the preamble might notbe long enough to obtain the needed accuracy for the carrier frequencyoffset estimate.

In Time Division Multiple Access (TDMA) systems, this does not cause asignificant problem as the residual CFO after preamble estimation can beviewed as a time-variant phase offset that can be tracked using datadecisions. Moreover, in TDMA systems, the phase variations over thepreamble duration is relatively negligible, thus a very accurate initialphase estimate can be obtained from the preamble. In CDMA systems,however, the known preamble spans a relatively longer period than thatof a corresponding TDMA system due to data spreading and possiblepreamble interleaving. In this case, any residual CFO can cause arelatively high phase variation, which prohibits accurate initial phaseestimation. Moreover, since in CDMA systems data and preamble aretransmitted at the same time, data symbols will suffer the same largephase variation as the preamble. In addition to that, any possibleresidual CFO can result in loss of orthogonality in the CDMA codes,which can cause significant inter-code-interference (ICI). CDMA basedcommunication systems need a much higher accuracy of carrier frequencyestimation than TDMA systems. In many cases, the preamble might not belong enough to provide such accuracy.

Further limitations and disadvantages of conventional and traditionalsystems will become apparent to one of skill in the art throughcomparison of such systems with the invention as set forth in theremainder of the present application with reference to the drawings

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theSeveral Views of the Drawings, the Detailed Description of theInvention, and the claims. Other features and advantages of the presentinvention will become apparent from the following detailed descriptionof the invention made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a system diagram illustrating an embodiment of a cable modem(CM) communication system that is built according to the presentinvention.

FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system that is built according to the present invention.

FIG. 3A is a system diagram illustrating an embodiment of a cellularcommunication system that is built according to the present invention.

FIG. 3B is a system diagram illustrating another embodiment of acellular communication system that is built according to the presentinvention.

FIG. 4 is a system diagram illustrating an embodiment of a satellitecommunication system that is built according to the present invention.

FIG. 5A is a system diagram illustrating an embodiment of a microwavecommunication system that is built according to the present invention.

FIG. 5B is a system diagram illustrating an embodiment of apoint-to-point radio communication system that is built according to thepresent invention.

FIG. 6 is a system diagram illustrating an embodiment of a highdefinition (HDTV) communication system that is built according to thepresent invention.

FIG. 7 is a system diagram illustrating an embodiment of a communicationsystem that is built according to the present invention.

FIG. 8 is a system diagram illustrating another embodiment of acommunication system that is built according to the present invention.

FIG. 9 is a system diagram illustrating an embodiment of a cable modemtermination system (CMTS) system that is built according to the presentinvention.

FIG. 10 is a system diagram illustrating an embodiment of a burstreceiver system that is built according to the present invention.

FIG. 11 is a diagram illustrating an embodiment of iterative data-aidedCFO estimation that is performed according to the present invention.

FIG. 12 is a diagram illustrating another embodiment of iterativedata-aided CFO estimation that is performed according to the presentinvention.

FIG. 13 is a flow diagram illustrating an embodiment of an iterativedata-aided CFO estimation method that is performed according to thepresent invention.

FIG. 14 is a flow diagram illustrating another embodiment of aniterative data-aided CFO estimation method that is performed accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a system diagram illustrating an embodiment of a CMcommunication system 100 that is built according to the presentinvention. The CM communication system includes a number of CMs (shownas a CM user #1 111, a CM user #2 115, . . . , and a CM user #n 121) anda CMTS 130. The CMTS 130 is a component that exchanges digital signalswith CMs on a cable network.

Each of a number of CM users, shown as the CM user #1 111, the CM user#2 115, . . . , and the CM user #n 121, is able to communicativelycouple to a CM network segment 199. A number of elements may be includedwithin the CM network segment 199, as understood by those persons havingskill in the art. For example, routers, splitters, couplers, relays, andamplifiers may be contained within the CM network segment 199 withoutdeparting from the scope and spirit of the invention.

The CM network segment 199 allows communicative coupling between a CMuser and a cable headend transmitter 120 and/or a CMTS 130. In someembodiments, a cable CMTS is in fact contained within a headendtransmitter. In other embodiments, a cable CMTS is located externallywith respect to a headend transmitter. For example, the CMTS 130 may belocated externally to a cable headend transmitter 120. In alternativeembodiments, a CMTS 135 may be located within the cable headendtransmitter 120. The CMTS 130 may be located at a local office of acable television company or at another location within a CMcommunication system. In the following description, the CMTS 130 is usedfor illustration; yet, those persons having skill in the art willappreciate that the same functionality and capability as described forthe CMTS 130 may equally apply to embodiments that alternatively employthe CMTS 135. The cable headend transmitter 120 is able to provide anumber of services including those of audio, video, local accesschannels, as well as any other service known in the art of cablesystems. Each of these services may be provided to the one or more CMusers 111, 115, . . . , and 121.

In addition, through the CMTS 130, the CM users 111, 115, . . . , 121are able to transmit and receive data from the Internet, . . . , and/orany other network to which the CMTS 130 is communicatively coupled. Theoperation of a CMTS, at the cable-provider's head-end, may be viewed asproviding many of the same functions provided by a digital subscriberline access multiplexor (DSLAM) within a digital subscriber line (DSL)system. The CMTS 130 takes the traffic coming in from a group ofcustomers on a single channel and routes it to an Internet ServiceProvider (ISP) for connection to the Internet, as shown via the Internetaccess. At the head-end, the cable providers will have, or lease spacefor a third-party ISP to have, servers for accounting and logging,dynamic host configuration protocol (DHCP) for assigning andadministering the Internet protocol (IP) addresses of all the cablesystem's users, and typically control servers for a protocol called DataOver Cable Service Interface Specifications (DOCSIS), the major standardused by U.S. cable systems in providing Internet access to users.

The downstream information flows to all of the connected CM users 111,115, . . . , 121; this may be viewed to be in a manner that is similarto that manner within an Ethernet network. The individual networkconnection, within the CM network segment 199, decides whether aparticular block of data is intended for it or not. On the upstreamside, information is sent from the CM users 111, 115, . . . , 121 to theCMTS 130; on this upstream transmission, the users within the CM users111, 115, . . . , 121 to whom the data is not intended do not see thatdata at all. As an example of the capabilities proffered by a CMTS, theCMTS will enable as many as 1,000 users to connect to the Internetthrough a single 6 MHz channel. Since a single channel is capable of30-40 megabits per second of total throughput, this means that users maysee far better performance than is available with standard dial-upmodems. Embodiments implementing the present invention are describedbelow and in the various Figures that show the data handling and controlwithin one or both of a CM and a CMTS within a CM system that operatesby employing SCDMA (Synchronous Code Division Multiple Access).

The CMs of the CM users 111, 115, . . . , 121 and the CMTS 130communicate synchronization information to one another to ensure properalignment of transmission from the CM users 111, 115, . . . , 121 to theCMTS 130. This is where the synchronization of the SCDMA communicationsystems is extremely important. When a number of the CMs all transmittheir signals at a same time such that these signals are received at theCMTS 130 on the same frequency and at the same time. they must all beable to be properly de-spread and decoded for proper signal processing.

Each of the CMs users 111, 115, . . . , 121 is located a respectivetransmit distance from the CMTS 130. In order to achieve optimumspreading diversity and orthogonality for the CMs users 111, 115, . . ., 121 to transmission of the CMTS 130, each of the CM transmissions mustbe synchronized so that it arrives, from the perspective of the CMTS130, synchronous with other CM transmissions. In order to achieve thisgoal, for a particular transmission cycle, each of the CMs 111, 115, . .. , 121 will typically transmit to the CMTS 130 at a respectivetransmission time, which will likely differ from the transmission timesof other CMs. These differing transmission times will be based upon therelative transmission distance between the CM and the CMTS 130. Theseoperations may be supported by the determination of the round tripdelays (RTPs) between the CMTS 130 and each supported CM. With theseRTPs determined, the CMs may then determine at what point to transmittheir SCDMA data so that all CM transmissions will arrive synchronouslyat the CMTS 130.

The present invention enables iterative data-aided CFO estimationbetween each of the CM users (CMs users 111, 115, . . . , 121) withinthe CMTS 130. All of the functionality described herein this patentapplication may be performed within the context of the CM communicationsystem of the FIG. 1. The FIG. 1 shows just one embodiment where thevarious aspects of the present invention may be implemented. Severalother embodiments are described as well.

FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system 200 that is built according to the presentinvention. From certain perspectives, the FIG. 2 may be viewed as acommunication system allowing bi-directional communication between acustomer premise equipment (CPE) 240 and a network. In some embodiments,the CPE 240 is a personal computer or some other device allowing a userto access an external network. The network may be a wide area network(WAN) 280, or alternatively, the Internet 290 itself. For example, theCM communication system 200 is operable to allow Internet protocol (IP)traffic to achieve transparent bi-directional transfer between aCMTS-network side interface (CMTS-NSI: viewed as being between the CMTS230 and the Internet 290) and a CM to CPE interface (CMCI: viewed asbeing between the CM 210 and the CPE 240).

The WAN 280, and/or the Internet 290, is/are communicatively coupled tothe CMTS 230 via a CMTS-NSI. The CMTS 230 is operable to support theexternal network termination, for one or both of the WAN 280 and theInternet 290. The CMTS 230 includes a modulator and a demodulator tosupport transmitter and receiver functionality to and from a CM networksegment 299. The receiver functionality within the CMTS 230 is operableto support iterative data-aided CFO estimation functionality for CDMA231 according to the present invention.

A number of elements may be included within the CM network segment 299,as understood by those persons having skill in the art. For example,routers, splitters, couplers, relays, and amplifiers may be containedwithin the CM network segment 299 without departing from the scope andspirit of the invention. The CM network segment 299 allows communicativecoupling between a CM user and the CMTS 230.

FIG. 3A is a system diagram illustrating an embodiment of a cellularcommunication system 300A that is built according to the presentinvention. A mobile transmitter 310 has a local antenna 311. The mobiletransmitter 310 may be any number of types of transmitters including acellular telephone, a wireless pager unit, a mobile computer havingtransmit functionality, or any other type of mobile transmitter. Themobile transmitter 310 transmits a signal, using its local antenna 311,to a base station receiver 340 via a wireless communication channel. Thebase station receiver 340 is communicatively coupled to a receivingwireless tower 349 to be able to receive transmission from the localantenna 311 of the mobile transmitter 310 that have been communicatedvia the wireless communication channel. The receiving wireless tower 349communicatively couples the received signal to the base station receiver340.

The base station receiver 340 is then able to support iterativedata-aided CFO estimation functionality for CDMA according to thepresent invention, as shown in a functional block 341, on the receivedsignal. The FIG. 3A shows just one of many embodiments where iterativedata-aided CFO estimation functionality for CDMA, performed according tothe present invention, may be performed to provide for improvedoperation within a communication system.

FIG. 3B is a system diagram illustrating another embodiment of acellular communication system that is built according to the presentinvention. From certain perspectives, the FIG. 3B may be viewed as beingthe reverse transmission operation of the cellular communication system300B of the FIG. 3A. A base station transmitter 320 is communicativelycoupled to a transmitting wireless tower 321. The base stationtransmitter 320, using its transmitting wireless tower 321, transmits asignal to a local antenna 339 via a wireless communication channel. Thelocal antenna 339 is communicatively coupled to a mobile receiver 330 sothat the mobile receiver 330 is able to receive transmission from thetransmitting wireless tower 321 of the base station transmitter 320 thathave been communicated via the wireless communication channel. The localantenna 339 communicatively couples the received signal to the mobilereceiver 330. It is noted that the mobile receiver 330 may be any numberof types of transmitters including a cellular telephone, a wirelesspager unit, a mobile computer having transmit functionality, or anyother type of mobile transmitter.

The base station receiver 340 is then able to support iterativedata-aided CFO estimation functionality for CDMA according to thepresent invention, as shown in a functional block 331, on the receivedsignal. The FIG. 3B shows just one of many embodiments where theiterative data-aided CFO estimation functionality for CDMA, performedaccording to the present invention, may be performed to provide forimproved operation within a communication system.

FIG. 4 is a system diagram illustrating an embodiment of a satellitecommunication system 400 that is built according to the presentinvention. A transmitter 420 is communicatively coupled to a wirednetwork 410. The wired network 410 may include any number of networksincluding the Internet, proprietary networks, and other wired networksas understood by those persons having skill in the art. The transmitter420 includes a satellite earth station 451 that is able to communicateto a satellite 453 via a wireless communication channel. The satellite453 is able to communicate with a receiver 430. The receiver 430 is alsolocated on the earth. Here, the communication to and from the satellite453 may cooperatively be viewed as being a wireless communicationchannel, or each of the communication to and from the satellite 453 maybe viewed as being two distinct wireless communication channels.

For example, the wireless communication “channel” may be viewed as notincluding multiple wireless hops in one embodiment. In otherembodiments, the satellite 453 receives a signal received from thesatellite earth station 451, amplifies it, and relays it to the receiver430; the receiver 430 may include terrestrial receivers such assatellite receivers, satellite based telephones, and satellite basedInternet receivers, among other receiver types. In the case where thesatellite 453 receives a signal received from the satellite earthstation 451, amplifies it, and relays it, the satellite 453 may beviewed as being a “transponder.” In addition, other satellites may existthat perform both receiver and transmitter operations. In this case,each leg of an up-down transmission via the wireless communicationchannel would be considered separately. The wireless communicationchannel between the satellite 453 and a fixed earth station would likelybe less time-varying than the wireless communication channel between thesatellite 453 and a mobile station.

In whichever embodiment, the satellite 453 communicates with thereceiver 430. The receiver 430 may be viewed as being a mobile unit incertain embodiments (employing a local antenna 412); alternatively, thereceiver 430 may be viewed as being a satellite earth station 452 thatmay be communicatively coupled to a wired network in a similar mannerthat the satellite earth station 451, within the transmitter 420,communicatively couples to a wired network. In both situations, thereceiver 430 is able to support iterative data-aided CFO estimationfunctionality for CDMA, as shown in a functional block 431, according tothe present invention. For example, the receiver 430 is able to performiterative data-aided CFO estimation functionality for CDMA, as shown ina functional block 431, on the signal received from the satellite 453.The FIG. 4 shows just one of many embodiments where the iterativedata-aided CFO estimation functionality for CDMA, performed according tothe present invention, may be performed to provide for improved receiverperformance.

FIG. 5A is a system diagram illustrating an embodiment of a microwavecommunication system 500A that is built according to the presentinvention. A tower transmitter 511 includes a wireless tower 515. Thetower transmitter 511, using its wireless tower 515, transmits a signalto a tower receiver 512 via a wireless communication channel. The towerreceiver 512 includes a wireless tower 516. The wireless tower 516 isable to receive transmissions from the wireless tower 515 that have beencommunicated via the wireless communication channel. The tower receiver512 is then able to support iterative data-aided CFO estimationfunctionality for CDMA, as shown in a functional block 533. The FIG. 5Ashows just one of many embodiments where iterative data-aided CFOestimation functionality for CDMA, performed according to the presentinvention, may be performed to provide for improved receiverperformance.

FIG. 5B is a system diagram illustrating an embodiment of apoint-to-point radio communication system 500B that is built accordingto the present invention. A mobile unit 551 includes a local antenna555. The mobile unit 551, using its local antenna 555, transmits asignal to a local antenna 556 via a wireless communication channel. Thelocal antenna 556 is included within a mobile unit 552. The mobile unit552 is able to receive transmissions from the mobile unit 551 that havebeen communicated via the wireless communication channel. The mobileunit 552 is then able to support iterative data-aided CFO estimationfunctionality for CDMA, as shown in a functional block 553, on thereceived signal. The FIG. 5B shows just one of many embodiments whereiterative data-aided CFO estimation functionality for CDMA, performedaccording to the present invention, may be performed to provide forimproved receiver performance.

FIG. 6 is a system diagram illustrating an embodiment of a highdefinition (HDTV) communication system 600 that is built according tothe present invention. An HDTV transmitter 610 includes a wireless tower611. The HDTV transmitter 610, using its wireless tower 611, transmits asignal to an HDTV set top box receiver 620 via a wireless communicationchannel. The HDTV set top box receiver 620 includes the functionality toreceive the wireless transmitted signal. The HDTV set top box receiver620 is also communicatively coupled to an HDTV display 630 that is ableto display the demodulated and decoded wireless transmitted signalsreceived by the HDTV set top box receiver 620.

The HDTV set top box receiver 620 is then able to support iterativedata-aided CFO estimation functionality for CDMA, as shown in afunctional block 623 to provide for improved receiver performance. TheFIG. 6 shows yet another of many embodiments where iterative data-aidedCFO estimation functionality for CDMA, performed according to thepresent invention, may be performed to provide for improved receiverperformance.

FIG. 7 is a system diagram illustrating an embodiment of a communicationsystem that is built according to the present invention. The FIG. 7shows communicative coupling, via a communication channel 799, betweentwo transceivers, namely, a transceiver 701 and a transceiver 702. Thecommunication channel 799 may be a wireline communication channel or awireless communication channel.

Each of the transceivers 701 and 702 includes a transmitter and areceiver. For example, the transceiver 701 includes a transmitter 749and a receiver 740; the transceiver 702 includes a transmitter 759 and areceiver 730. The receivers 740 and 730, within the transceivers 701 and702, respectively, are each operable to support iterative data-aided CFOestimation functionality for CDMA according to the present invention.This will allow improved signal processing for both of the transceivers701 and 702. For example, the receiver 740, within the transceiver 701,is able to support iterative data-aided CFO estimation functionality forCDMA, as shown in a functional block 741, on a signal received from thetransmitter 759 of the transceiver 702. Similarly, the receiver 730,within the transceiver 702, is able to support iterative data-aided CFOestimation functionality for CDMA, as shown in a functional block 731,on a signal received from the transmitter 749 of the transceiver 701.The FIG. 7 shows yet another of many embodiments where iterativedata-aided CFO estimation functionality for CDMA, performed according tothe present invention, may be performed to provide for improvedperformance.

FIG. 8 is a system diagram illustrating another embodiment of acommunication system 800 that is built according to the presentinvention. The FIG. 8 shows communicative coupling, via a communicationchannel 899, between a transmitter 849 and a receiver 830. Thecommunication channel 899 may be a wireline communication channel or awireless communication channel. The receiver 830 is operable to supportiterative data-aided CFO estimation functionality for CDMA, as shown ina functional block 831, according to the present invention. The FIG. 8shows yet another of many embodiments where iterative data-aided CFOestimation functionality for CDMA, performed according to the presentinvention, may be performed to provide for improved performance.

FIG. 9 is a system diagram illustrating an embodiment of a CMTS system900 that is built according to the present invention. The CMTS system900 includes a CMTS medium access controller (MAC) 930 that operateswith a number of other devices to perform communication from one or moreCMs to a WAN 980. The CMTS MAC 930 may be viewed as providing thehardware support for MAC-layer per-packet functions includingfragmentation, concatenation, and payload header suppression that allare able to offload the processing required by a system centralprocessing unit (CPU) 972. This will provide for higher overall systemperformance. In addition, the CMTS MAC 930 is able to provide supportfor carrier class redundancy via timestamp synchronization across anumber of receivers, shown as a receiver 911, a receiver 911, and areceiver 913 that are each operable to receive upstream analog inputs.In certain embodiments, each of the receivers 911, 912, and 913 are dualuniversal advanced TDMA/CDMA (Time Division Multiple Access/CodeDivision Multiple Access) PHY-layer burst receivers. That is top say,each of the receivers 911, 912, and 913 includes at least one TDMAreceive channel and at least one CDMA receive channel; in tic case, eachof the receivers 911, 912, and 913 may be viewed as being multi-channelreceivers. In other embodiments, the receivers 911, 912, and 913includes only CDMA receive channels.

In addition, the CMTS MAC 930 may be operated remotely with arouting/classification engine 979 that is located externally to the CMTSMAC 930 for distributed CMTS applications including mini fiber nodeapplications. Moreover, a Standard Programming Interface (SPI) masterport may be employed to control the interface to the receivers 911, 912,and 913 as well as to a downstream modulator 920.

The CMTS MAC 930 may be viewed as being a highly integrated CMTS MACintegrated circuit (IC) for use within the various DOCSIS and advancedTDMA/CDMA physical layer (PHY-layer) CMTS products. The CMTS MAC 930employs sophisticated hardware engines for upstream and downstreampaths. The upstream processor design is segmented and uses two banks ofSynchronous Dynamic Random Access Memory (SDRAM) to minimize latency oninternal buses. The two banks of SDRAM used by the upstream processorare shown as upstream SDRAM 975 (operable to support keys andreassembly) and SDRAM 976 (operable to support Packaging, Handling, andStorage (PHS) and output queues). The upstream processor performs DataEncryption Standard (DES) decryption, fragment reassembly,de-concatenation, payload packet expansion, packet acceleration,upstream Management Information Base (MIB) statistic gathering, andpriority queuing for the resultant packets. Each output queue can beindependently configured to output packets to either a Personal ComputerInterface (PCI) or a Gigabit Media Independent Interface (GMII). DOCSISMAC management messages and bandwidth requests are extracted and queuedseparately from data packets so that they are readily available to thesystem controller.

The downstream processor accepts packets from priority queues andperforms payload header suppression, DOCSIS header creation, DESencryption, Cyclic Redundancy Check (CRC) and Header Check Sequence (ofthe DOCSIS specification), Moving Pictures Experts Group (MPEG)encapsulation and multiplexing, and timestamp generation on the in-banddata. The CMTS MAC 930 includes an out-of-band generator and CDMAPHY-layer (and/or TDMA PHY-layer) interface so that it may communicatewith a CM device's out-of-band receiver for control of power managementfunctions. The downstream processor will also use SDRAM 977 (operable tosupport PHS and output queues). The CMTS MAC 930 may be configured andmanaged externally via a PCI interface and a PCI bus 971.

Each of the receivers 911, 912, and 913 is operable to support iterativedata-aided CFO estimation functionality for CDMA. For example, thereceiver 911 is operable to support iterative data-aided CFO estimationfunctionality for CDMA, as shown in a functional block 991; the receiver912 is operable to support iterative data-aided CFO estimationfunctionality for CDMA, as shown in a functional block 992; and thereceiver 913 is operable to support iterative data-aided CFO estimationfunctionality for CDMA, as shown in a functional block 993. The FIG. 9shows yet another embodiment in which iterative data-aided CFOestimation functionality for CDMA may be performed according to thepresent invention. Any of the functionality and operations described inthe other embodiments may be performed within the context of the CMTSsystem 900 without departing from the scope and spirit of the invention.

FIG. 10 is a system diagram illustrating an embodiment of a burstreceiver system 1000 that is built according to the present invention.The burst receiver system 1000 includes at least one multi-channelreceiver 1010. The multi-channel receiver 1010 is operable to receive anumber of upstream analog inputs that are transmitted from CMs. Theupstream analog inputs may be in the form of either TDMA (Time DivisionMultiple Access) and/or CDMA (Code Division Multiple Access) format. Anumber of receive channels may be included within the multi-channelreceiver 1010. The FIG. 10 shows a particular embodiment where themulti-channel receiver 1010 includes a number of CDMA receive channels.

For example, the multi-channel receiver 1010 is operable to support anumber of CDMA receive channels 1020 (shown as CDMA signal 1 and CDMAsignal 2) and to support iterative data-aided CFO estimationfunctionality, as shown in a functional blocks 1021, for those receivedCDMA signals. In addition, the multi-channel receiver 1010 is operableto support a number of CDMA receive channels 1030 (shown as CDMA signal3 and CDMA signal 4) and to support iterative data-aided CFO estimationfunctionality, as shown in a functional blocks 1031, for those receivedCDMA signals; the multi-channel receiver 1010 is operable to support anumber of CDMA receive channels 1040 (shown as CDMA signal N and CDMAsignal N−1) and to support iterative data-aided CFO estimationfunctionality, as shown in a functional blocks 1041, for those receivedCDMA signals.

Generically speaking, the multi-channel receiver 1010 is operable tosupport a number of receive channels and to support iterative data-aidedCFO estimation functionality for CDMA for those received signals. Themulti-channel receiver 1010 of the FIG. 10 is operable to interface witha CMTS MAC. Those persons having skill in the art will appreciate thatthe burst receiver system 1000 may include a number of multi-channelreceivers that are each operable to interface with the CMTS MAC.

In certain embodiments, the multi-channel receiver 1010 proffers anumber of various functionalities. The multi-channel receiver 1010 maybe a universal headend advanced TDMA PHY-layer QPSK/QAM (QuadraturePhase Shift Keying/Quadrature Amplitude Modulation) burst receiver; themulti-channel receiver 1010 also include functionality to be a universalheadend advanced CDMA PHY-layer QPSK/QAM burst receiver; or themulti-channel receiver 1010 also include functionality to be a universalheadend advanced TDMA/CDMA PHY-layer QPSK/QAM burst receiver offeringboth TDMA/CDMA functionality. The multi-channel receiver 1010 may beDOCSIS/EuroDOCSIS based, IEEE 802.14 compliant. The multi-channelreceiver 1010 may be adaptable to numerous programmable demodulationincluding BPSK (Binary Phase Shift Keying), and/or QPSK,8/16/32/64/128/256/516/1024 QAM. The multi-channel receiver 1010 isadaptable to support variable symbols rates as well. Other functionalitymay likewise be included to the multi-channel receiver 1010 withoutdeparting from the scope and spirit of the invention. Those personshaving skill in the art will recognize that such variations andmodifications may be made to the communication receiver.

FIG. 11 is a diagram illustrating an embodiment of iterative data-aidedCFO estimation 1100 that is performed according to the presentinvention. Received data includes a data portion and a preamble portionwithin CDMA systems. The preamble portion is extracted, and theextracted preamble sequence is partitioned into a number of subgroups,shown as a subgroup 1 . . . N. Each of the subgroups includes a numberof preamble symbols, shown as 1 . . . M. The number of preamble symbolsM may be substantially optimized for the number of subgroups N;alternatively, the number of preamble symbols M may be predetermined andfixed irrespective of the number of subgroups N. A subgroup average iscalculated for each of the averages. Here, a subgroup average sequenceis then generated that is composed of the averages for the subgroups 1 .. . N; this is shown as a subgroup average 1, a subgroup average 2, . .. , a subgroup average N. Phase differentials are then determinedbetween each of the subgroup averages 1 . . . N, shown as a phasedifferential 1, phase differential 2, . . . , phase differential N−1. ACFO estimate is then determined by employing averaging each of the phasedifferentials.

After a CFO estimate is generated using the iterative data-aided CFOestimation 1100 shown in the FIG. 11, then the entire portion of datathat is received may be corrected using this initial estimate of theCFO. Therefore, this initial CFO estimate is used to correct the wholedespread data. The corrected data, using the initial CFO estimate, isthen sliced. Each despread data symbol is divided by the correspondingsliced data decision. The obtained sequence is then averaged acrossdifferent codes to obtain a less noisy sequence, which is then used toestimate the CFO again. The procedure can be repeated (iterated) toobtain a more accurate carrier frequency offset estimate; the number oftimes in which the procedure is repeated may be programmable orpredetermined. The FIG. 11 shows the very first iteration of generatinga CFO estimate. Those persons having skill in the art will recognize howthe iterative data-aided CFO estimation 1100 may be performed multipletimes in an iterative manner to provide for an even better CFO estimatefor a CDMA system. The FIG. 11 shows yet another of the many embodimentswhere iterative data-aided CFO estimation functionality for CDMA may beperformed according to the present invention.

FIG. 12 is a diagram illustrating another embodiment of iterativedata-aided CFO estimation 1200 that is performed according to thepresent invention. The FIG. 12 shows just one schematic diagram of theproposed CFO estimation method. The details of the CFO estimation may bedescribed as follows: a two-step CFO estimation is used. The first stepinvolves estimating the CFO from the preamble only, correcting for it,and slicing the data. The second step is to use the sliced data (or harddecisions) to estimate the CFO again. The second step can be repeatedmore than once if needed or desired. The details of the two proceduresteps are given as follows.

Given a received preamble despread sequence {x₁, x₂, . . . , x_(L)},where L is the preamble length, the CFO is to be estimated. In thisillustration, it is assumed that the preamble extends only over onecode; clearly other embodiments are envisioned within the scope andspirit of the invention as well. The angular CFO estimate ω is computedas follows: The preamble symbols are first removed to get the sequence{y_(i)=x_(i)/p_(i)}, where {p_(i)} is the preamble sequence. Thesequence {y_(i)} is then divided into N subgroups, with M symbols ineach subgroup, such that N=L/M. Each subgroup is averaged to get asequence {Z_(i)} of N elements. The phase differential between z_(i) andZ_(i+1) is obtained, to get N−1 phase differentials and then the angularfrequency offset ω as shown below:

φ_(i) = angle  (z_(i + 1)z_(i)^(*)), i = 1⋯  N − 1$\omega = {\frac{1}{\left( {N - 1} \right) \cdot M \cdot I}{\sum\limits_{i = 1}^{N - 1}\varphi_{i}}}$

where I is the interleaving depth. Similar to other embodimentsdescribed above, the value of M may be optimized for various values ofN; alternatively, the value of M may be predetermined and fixedirrespective of the value of N. In addition, the value of N may beoptimized for each given value of L; alternatively, the value of N maybe fixed irrespective of the value of L. The received preamble sequenceis then corrected for the frequency offset as shown below:y′ _(i) =y _(i)×exp{−j[ω·(i−0.5)]},i=1 . . . L

The carrier phase (φ) and amplitude (α) are estimated as follows

$\phi = {{angle}\mspace{11mu}\left( {\frac{1}{L}{\sum\limits_{i = 1}^{L - 1}y_{i}^{\prime}}} \right)}$$\alpha = \sqrt{\frac{1}{L}{\sum\limits_{i = 1}^{L - 1}{y_{i}^{\prime}}^{2}}}$

The despread sequence {r_(k,c)} for each user is then corrected for theCFO to obtain the corrected soft decision sequence {S_(k,c)} as shownbelow:

${s_{k,c} = {r_{k,c} \times \frac{1}{\alpha}\exp\left\{ {- {j\left\lbrack {{\omega \cdot \left( {k - 0.5} \right)} - \phi} \right\rbrack}} \right\}}},{k = {1\cdots\mspace{11mu} K}},{c = {1\cdots\mspace{11mu} C}}$

where C is the number of codes of the desired user and K is the numberof symbols per frame. The de-rotated sequence is then sliced to obtaindata hard decisions {h_(k,c)} as shown below:h _(k,c)=slice(s _(k,c)),k=1 . . . K,c=1 . . . C

The de-rotated soft decisions are averaged across codes to obtain a1-row sequence as shown below:

${d_{k} = {\frac{1}{C}{\sum\limits_{c = 1}^{C}\left( {s_{k,c}/h_{k,c}} \right)}}},{k = {1\cdots\mspace{11mu} K}}$

It is also noted that preamble sequence is included in this average withthe hard decisions being replaced by the known preamble symbols. Thepreamble portion can also be weighted by a larger weight than the dataif desired in certain embodiments.

The sequence {d_(k)} is divided into N subgroups, with M symbols in eachsubgroup, such that N=K/M. Each subgroup is averaged to get a sequence{w_(i)} of N elements. The phase differential between w_(k) and w_(k+1)is obtained, to get N−1 phase differentials and then the angularfrequency offset ω as shown below:

φ_(k) = angle  (z_(k + 1) z_(k)^(*)), k = 1 ⋯  N − 1$\omega = {\frac{1}{\left( {N - 1} \right) \cdot M}\;{\sum\limits_{k = 1}^{N - 1}\varphi_{k}}}$

The value of N can be optimized for each given value of K. Similar toother embodiments described above, the value of N may be optimized forvarious values of K. In the FIG. 12, the number of subgroups N=4, thenumber of symbols in each subgroup M=2, and the value of K=8. The sameprocedure can be repeated a number of times to obtain better frequency,phase, and gain estimates, if desired.

FIG. 13 is a flow diagram illustrating an embodiment of an iterativedata-aided CFO estimation method 1300 that is performed according to thepresent invention. In a block 1310, a packet is received. This packetmay be viewed as being a CDMA data packet. Within a block 1320, apreamble sequence is extracted from the received CDMA data packet. Then,preamble processing is performed on the preamble sequence of thereceived CDMA data packet to generate phase differentials. Using thephase differentials generated in the block 1330, CFO estimation isperformed in a block 1340. Then, using this initial CFO estimate thathas been generated in the block 1340, the whole despread data iscorrected using this initial CFO estimate in a block 1350. Afterwards, asingle row sequence is obtained from the now corrected data within ablock 1360. Using this single row, then 1-row sequence processing isperformed again to generate a second group of phase differentials in ablock 1370.

Using the results of this 1-row sequence processing is used tore-estimate the CFO of the received CDMA data packet. If desired inalternative embodiments, the iterative data-aided CFO estimation method1300 may return to the block 1350 Q number of times to perform more thana single iteration of correction to the data using a CFO estimate.Clearly, any number of iterations may be employed without departing fromthe scope and spirit of the invention. The FIG. 13 shows one manner inwhich iterative data-aided CFO estimation may be performed according tothe present invention. From one perspective, the iterative data-aidedCFO estimation method 1300 shows an embodiment of performingprogrammable iterative data-aided CFO estimation for CDMA where thenumber of iterations may be controlled to provide for improvedperformance while also efficiently allocating processing resources.

FIG. 14 is a flow diagram illustrating another embodiment of aniterative data-aided CFO estimation method 1400 that is performedaccording to the present invention. Within the FIG. 14, an iterativedata-aided CFO estimation method is described. The details of theestimation method may be described as follows: a two-step iterativedata-aided CFO estimation method is used. The first step involvesestimating the CFO from the preamble only, correcting for it, andslicing the data. The second step is to use the sliced data (or harddecisions) to estimate the CFO again. The second step can be repeatedmore than once if needed. The details of the two procedure steps may bedescribed within the steps described below: in a block 1410, a CDMA datapacket is received. In a block 1420, a preamble sequence is extractedfrom the received CDMA data packet. In certain embodiments, as shown ina block 1421, a received preamble despread sequence {x_(i)}={x₁, x₂, . .. x_(L)} is extracted from the received CDMA data packet, where L is thepreamble length. This received preamble despread sequence {x_(i)} isused to generate an initial CFO estimate. It is noted that it is assumedthat the preamble extends only over one code; however, other embodimentsare also envisioned within the scope and spirit of the invention.

The angular CFO estimate ω then is computed as follows: in a block 1430,the extracted preamble symbols are modified using a known preamblesequence {p_(i)}. As shown in a block 1431 in certain embodiments, thepreamble symbols are first removed to get the sequence{y_(i)=x_(i)/p_(i)}, where {p_(i)} is the preamble sequence. Then, in ablock 1440, the sequence {y_(i)} is divided into N subgroups, with Msymbols in each subgroup, such that N=L/M. Each subgroup is averaged toget a sequence {z_(i)} of N elements as shown in a block 1450. In ablock 1460, the phase differential between z_(i) and z_(i+1) isobtained, to get N−1 phase differentials. Then, the angular CFO ω iscalculated in a block 1470 as shown below:

φ_(i) = angle  (z_(i + 1)z_(i)^(*)), i = 1⋯  N − 1$\omega = {\frac{1}{\left( {N - 1} \right) \cdot M \cdot I}{\sum\limits_{i = 1}^{N - 1}\varphi_{i}}}$

where I is the interleaving depth. The value of N can be optimized foreach given value of L. Now the second step of the two-step iterativedata-aided CFO estimation is performed in the following steps. Thereceived preamble sequence is then corrected for the CFO in a block 1471as shown below.y′ _(i) =y _(i)×exp{−j[ω·(i−0.5)]},i=1 . . . L

The carrier phase and amplitude are estimated as shown in a block 1472as shown below:

$\phi = {{angle}\mspace{11mu}\left( {\frac{1}{L}{\sum\limits_{i = 1}^{L - 1}y_{i}^{\prime}}} \right)}$$\alpha = \sqrt{\frac{1}{L}{\sum\limits_{i = 1}^{L - 1}{y_{i}^{\prime}}^{2}}}$

In a block 1473, the despread sequence {r_(k,c)} for each user is thencorrected for the frequency offset to obtain the corrected soft decisionsequence {s_(k,c)} as shown below:

${s_{k,c} = {r_{k,c} \times \frac{1}{\alpha}\exp\left\{ {- {j\left\lbrack {{\omega \cdot \left( {k - 0.5} \right)} - \phi} \right\rbrack}} \right\}}},{k = {1\cdots\mspace{11mu} K}},{c = {1\cdots\mspace{11mu} C}}$

where C is the number of codes of the desired user and K is the numberof symbols per frame. The de-rotated sequence is then sliced to obtaindata hard decisions {h_(k,c)} as shown in a block 1474 and as describedbelow:h _(k,c)=slice(s_(k,c)),k=1 . . . K,c=1 . . . C

The de-rotated soft decisions are averaged across codes to obtain a1-row sequence as shown in a block 1475 and as described below:

${d_{k} = {\frac{1}{C}{\sum\limits_{c = 1}^{C}\left( {s_{k,c}/h_{k,c}} \right)}}},{k = {1\cdots\mspace{11mu} K}}$

It is also noted that the preamble sequence is included in this averagewith the hard decisions being replaced by the known preamble symbols.The preamble portion can also be weighted by a larger weight than thedata if desired in certain embodiments. The sequence {d_(k)} is dividedinto N subgroups, with M symbols in each subgroup, such that N=K/M asshown in a block 1476. Each subgroup is averaged to get a sequence{w_(i)} of N elements as shown in a block 1477. The phase differentialbetween w_(k) and w_(k+1) is obtained, to get N−1 phase differentials asshown in a block 1478 and as described below.φ_(k)=angle(z _(k+1) z* _(k)),k=1 . . . N−1

Then the angular CFO ω is calculated as shown in a block 1479 and asdescribed below:

$\omega = {\frac{1}{\left( {N - 1} \right) \cdot M}\;{\sum\limits_{k = 1}^{N - 1}\varphi_{k}}}$

The value of N can be optimized for each given value of K. The sameprocedure can be repeated to obtain better frequency, phase, and gainestimates. The number of iterations that may be performed according tothe present invention is programmable and may generically be describedas Q times. The iterative data-aided CFO estimation method 1400, afterperforming the operation of the block 1479, may then return to theoperation within the block 1471. When Q=1, this may be viewed as being asingle iteration within the iterative data-aided CFO estimation of theFIG. 14.

The FIG. 14 shows yet another manner in which iterative data-aided CFOestimation may be performed according to the present invention.

The present invention provides for iterative data-aided CFO estimationin a manner that provides a better performance compared to two other CFOestimation methods (KAY and Fitz) as well as that provided by the CramerRao Bound. The KAY and Fitz CFO estimation methods are described in thefollowing article: Umberto Mengali and M. Morelli. “Data-Aided FrequencyEstimation for Burst Digital Transmission,” IEEE Transactions onCommunications, vol. 45, no. 1, pp. 23-25, January 1997. Iterativedata-aided CFO estimation, according to the present invention,significantly enhances accuracy especially for high SNR. The presentinvention provides a relatively higher accuracy than known carrierfrequency estimation methods. The present invention also provides for ahigh degree of flexibility in compromising performance and complexity.The present invention, in performing iterative data-aided CFO estimationfunctionality for CDMA, provides for a relatively higher accuracy thanpreamble-only frequency estimation approaches.

In view of the above detailed description of the invention andassociated drawings, other modifications and variations will now becomeapparent to those skilled in the art. It should also be apparent thatsuch other modifications and variations may be effected withoutdeparting from the spirit and scope of the invention.

1. A communication device, comprising: an input that is operable toreceive a signal from a communication channel, the signal including acode division multiple access (CDMA) data packet having a preambleportion and a data portion; and an iterative data-aided carrierfrequency offset (CFO) module that is operable to: generate a first CFOestimate of the CDMA data packet using the preamble portion; employ thefirst CFO estimate to correct for CFO within the data portion of theCDMA packet; and generate a second CFO estimate of the CDMA packet usingthe CFO corrected data portion.
 2. The communication device of claim 1,wherein: the iterative data-aided CFO module is operable to generate thesecond CFO estimate of the CDMA packet using the CFO corrected dataportion and the preamble.
 3. The communication device or claim 1,wherein: the iterative data-aided CFO module is operable to employ thesecond CFO estimate to re-correct for CFO within the data portion of theCDMA packet; and generate a third CFO estimate of the CDMA packet usingthe CFO re-corrected data portion.
 4. The communication device of claim1, wherein: the iterative data-aided CFO module is operable to perform apredetermined plurality of iterations when generating CFO estimates. 5.The communication device of claim 1 wherein: the iterative data-aidedCFO module is operable to perform a programmed plurality of iterationswhen generating CFO estimates.
 6. The communication device of claim 1,wherein; the iterative data-aided CFO module is operable to: modify thepreamble portion using an expected preamble portion; subgroup themodified preamble portion into a plurality of subgroups; calculate aplurality of phase averages such that each phase average corresponds toone subgroup of the plurality of subgroups; calculate a plurality ofphase differentials such that each phase differential is a phase averagedifference between two adjacent subgroups of the subgroups; and employthe plurality of phase differentials to generate at least one of thefirst CFO estimate and the second CFO estimate.
 7. The communicationdevice of claim 1, wherein: the communication device is operable todemodulate the signal using at least one of Binary Phase Shift Keying(BPSK), Quadrature Phase Shift Keying (QPSK), 16 Quadrature AmplitudeModulation (QAM), QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and1024 QAM.
 8. The communication device of claim 1, wherein: thecommunication device is a multi-channel communication device; a firstchannel of the multi-channel communication device is operable to receivethe signal including the CDMA data packet; and a second channel of themulti-channel communication device is operable to receive at least oneadditional signal that includes a time division multiple access (TDMA)data packet.
 9. The communication device of claim 1, wherein: thecommunication device is a wireless communication device that isimplemented within a wireless communication system.
 10. Thecommunication device of claim 1, wherein: the communication device is atleast one of a multi-channel headend physical layer burst receiver, abase station receiver, a mobile receiver, a satellite earth station, atower receiver, and a high definition television set top box receiver.11. A communication device, comprising: an input that is operable toreceive a signal from a communication channel, the signal including acode division multiple access (CDMA) data packet having a preambleportion and a data portion; and an iterative data-aided carrierfrequency offset (CFO) module that is operable to: generate a first CFOestimate of the CDMA data packet using the preamble portion; employ thefirst CFO estimate to correct for CFO within the data portion of theCDMA packet; and generate a second CFO estimate of the CDMA packet usingthe CFO corrected data portion and the preamble.
 12. The communicationdevice of claim 11, wherein: the iterative data-aided CFO module isoperable to employ the second CFO estimate to re-correct for CFO withinthe data portion of the CDMA packet; and generate a third CFO estimateof the CDMA packet using the CFO re-corrected data portion and thepreamble.
 13. The communication device of claim 11, wherein: theiterative data-aided CFO module is operable to perform a predeterminedplurality of iterations or a programmed plurality of iterations whengenerating CFO estimates.
 14. The communication device of claim 11,wherein: the communication device is a multi-channel communicationdevice; a first channel of the multi-channel communication device isoperable to receive the signal including the CDMA data packet; and asecond channel of the multi-channel communication device is operable toreceive at least one additional signal that includes a time divisionmultiple access (TDMA) data packet.
 15. The communication device ofclaim 11, wherein: the communication device is a wireless communicationdevice that is implemented within a wireless communication system. 16.The communication device of claim. 11, wherein: the communication deviceis at least one of a multi-channel headend physical layer burstreceiver, a base station receiver, a mobile receiver, a satellite earthstation, a tower receiver, and a high definition television set top boxreceiver.
 17. A method, comprising: receiving a signal from acommunication channel, wherein the signal includes a code divisionmultiple access (CDMA) data packet having a preamble portion and a dataportion; generating a first CFO estimate of the CDMA data packet usingthe preamble portion; employing the first CFO estimate to correct forCFO within the data portion of the CDMA packet; and generating a secondCFO estimate of the CDMA packet using the CFO corrected data portion.18. The method of claim 17, wherein: the generating the second CFOestimate of the CDMA packet is performed using both the CFO correcteddata portion and the preamble.
 19. The method of claim 17, furthercomprising: employing the second CFO estimate to re-correct for CFOwithin the data portion of the CDMA packet; and generating a third CFOestimate of the CDMA packet using the CFO re-corrected data portion andthe preamble.
 20. The method of claim 17, wherein: the method isperformed within a communication device; the communication device is awireless communication device that is implemented within a wirelesscommunication system.